PostgreSQL : Types of Shutdown

There are different ways to make a database shutdown for every database type whether it is MySQL, Oracle, MongoDB, etc, in PostgreSQL as well, there are 3 types of shutdown based on the signal provided

1.    SIGTERM

2.    SIGINT

3.    SIGQUIT

 

We will discuss them one by one

SIGTERM

This type of shutdown is identified as a smart shutdown

After receiving a shutdown signal, SIGTERM 

disallows new connections

let’s existing connection works normally 

shuts down only after sessions are terminated 

If the server is in online backup mode

It additionally waits until the online backup mode is no longer active, new connections still are allowed for superusers only, as they might need to send a request to disable the are online backup mode

If the server is in recovery mode

The recovery process will be stopped only after all regular sessions are terminated.

 

SIGINT

This mode is termed fast shutdown mode

once a SIGINT signal is sent, it

disallows new connections and sends all existing server processes SIGTERM, which makes them abort respective current transactions and exit promptly 

waits until all server process to exit and finally shuts down. 

if the server is in online backup mode

the backup mode will be terminated and the backup will be made useless

SIGQUIT

This mode is termed immediate shutdown mode

The server will send SIGQUIT to all the child processes and wait for them to terminate  and if it is not terminated within 5 sec, it sends SIGKILL

After forcing SIGQUIT,

the database needs recovery on the next startup

only recommended in case of emergency.